Author/Authors :
AI-Kahali, M.S.N. Sana a University - Faculty of Science - Department of Chemistry, Sana a , Ridley, T. University of Edinburgh - School of Chemistry, Scotland , Lawley, K.P. University of Edinburgh - School of Chemistry, Scotland , Donovan, R.J. University of Edinburgh - School of Chemistry, Scotland
Abstract :
The fragmentation processes of the aromatic conjugated diene systems have been studied by many research groups
[1-10]. Derrick et ale [1], have studied the electronic structure using photoelectron spectroscopy, where a number of
highly excited Rydberg states were accessed, also they attributed the fragmentation of the furan molecule to the
photoelectron energy responsible for the breaking ofthe C-C bond or the c-o bond. Rockwood et ale [10], using a fixed
frequency KrF laser (249 nm), and Zandee and Bernstein [4], using nitrogen laser pumped dye laser, both found
extensive ion fragmentation as the laser power density was increased. Cooper et ale [5] studied the fragmentation process
ofthe benzene, pyrrole, and furan molecules using the resonantly enhanced multiphoton ionization technique; they stated
that the fragmentation process for benzene was efficient at the highest laser power density 5 x 109 W/cm2
, for furan
molecule at a laser wavelength of 376 nm, in a two-photon resonance the parent ion was seen as the strongest peak,
while at 550.5 nm in a three-photon resonance the parent ion was not seen in full laser power, and only appeared slightly
at 54% ofthe laser power. Boesl et ale [6], in a work done on the fragmentation offuran, reported a weak dependence of
the ion efficiency on wavelength.
Here in this study, the fragmentation of the furan molecule was examined, using jet-cooling, resonance enhanced
multi photon ionization REMPI, combined with TOF mass spectrometry.
Multiphoton mass spectrometry relies on lasers to tune to a resonant state as an intermediate step on the way to
ionization with a further photon. This is essential as it is not only assures selectivity of the ionization events but also
greatly reduces the intensity required for ionization. If the laser wavelength is not resonant with an absorbing molecular
intermediate state, absorption of laser wavelength can still occur via virtual states, but at much higher levels of
intensities. At high enough laser intensities, everything ionizes, even the background gas in the ion source. Once this
non-discriminate excitation reaches ionization, extreme fragmentation usually results [11].
